User terminal and radio communication method

ABSTRACT

The present invention is designed to adequately control the transmission of uplink control information (UCI) using UL control channels. According to the present invention, a user terminal has a transmission section that transmits uplink control information (UCI), and a control section that determines a format of an uplink (UL) control channel that is used to transmit the UCI, from a plurality of formats, including a first format, in which the UCI and a reference signal are frequency-division-multiplexed, and a second format, in which the UCI and the reference signal are time-division-multiplexed.

TECHNICAL FIELD

The present invention relates to a user terminal and a radiocommunication method in next-generation mobile communication systems.

BACKGROUND ART

In the UMTS (Universal Mobile Telecommunications System) network, thespecifications of long-term evolution (LTE) have been drafted for thepurpose of further increasing high speed data rates, providing lowerlatency and so on (see non-patent literature 1). In addition, successorsystems of LTE are also under study for the purpose of achieving furtherbroadbandization and increased speed beyond LTE (referred to as, forexample, “LTE-A (LTE-Advanced),” “FRA (Future Radio Access),” “4G,”“5G,” “5G+(plus),” “NR (New RAT),” “LTE Rel. 14,” “LTE Rel. 15 (or laterversions),” and so on).

In existing LTE systems (for example, LTE Rel. 8 to 13), downlink (DL)and/or uplink (UL) communication are performed using one-ms subframes(also referred to as “transmission time intervals (TTIs)” and so on).These subframes are the time unit for transmitting one channel-encodeddata packet, and serve as the unit of processing in, for example,scheduling, link adaptation, retransmission control (HARQ: HybridAutomatic Repeat reQuest) and so on.

Also, in existing LTE systems (for example, LTE Rel. 8 to 13), a userterminal transmits uplink control information (UCI) by using a ULcontrol channel (for example, PUCCH: Physical Uplink Control Channel) ora UL data channel (for example, PUSCH: Physical Uplink Shared Channel).The format of this UL control channel is referred to as “PUCCH format”and so on.

UCI includes at least one of a scheduling request (SR), retransmissioncontrol information (HARQ-ACK (Hybrid Automatic RepeatreQuest-Acknowledgement), ACK and/or NACK (Negative ACK)) in response toDL data (DL data channel (for example, PDSCH: Physical Downlink SharedChannel)), and channel state information (CSI).

CITATION LIST Non-Patent Literature

Non-Patent Literature 1: 3GPP TS36.300 V8.12.0 “Evolved UniversalTerrestrial Radio Access (E-UTRA) and Evolved Universal TerrestrialRadio Access Network (E-UTRAN); Overall description; Stage 2 (Release8),” April, 2010

SUMMARY OF INVENTION Technical Problem

It is assumed that future radio communication systems (for example, LTERel. 14, LTE Rel. 15 (or later versions), 5G, NR, etc.) will transmitUCI using a UL control channel of a different format than existing LTEsystems (for example, LTE Rel. 13 and/or earlier versions).

For example, the PUCCH formats for use in existing LTE systems arecomprised of one-ms subframe units. Meanwhile, for future radiocommunication systems, a study is in progress to support a UL controlchannel having a shorter duration than existing LTE systems (hereinafteralso referred to as a “short PUCCH”). In addition, this short PUCCH mayaccommodate a plurality of formats that, for example, use differentmethods of multiplexing reference signals (which are referred to as“RSs,” and include, for example, the demodulation reference signal(DM-RS), which is used to demodulate UCI, the channel state soundingreference signal (SRS), and so on).

Thus, if multiple formats are supported for UL control channels (forexample, a short PUCCH) of different formats than existing LTE systems,there is a risk that user terminals may not be able to properly controlthe transmission of UCI using these UL control channels.

The present invention has been made in view of the above, and it istherefore an object of the present invention to provide a user terminaland a radio communication method, whereby UCI transmission using ULcontrol channels can be controlled adequately.

Solution to Problem

According to one aspect of the present invention, a user terminal has atransmission section that transmits uplink control information (UCI),and a control section that determines a format of an uplink (UL) controlchannel that is used to transmit the UCI, from a plurality of formats,including a first format, in which the UCI and a reference signal arefrequency-division-multiplexed, and a second format, in which the UCIand the reference signal are time-division-multiplexed.

Advantageous Effects of Invention

According to the present invention, user terminals can adequatelycontrol the transmission of uplink control information (UCI) using ULcontrol channels.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B provide diagrams, each showing an example of the formatof a UL control channel;

FIGS. 2A and 2B provide diagrams, each showing an example of the formatof a short PUCCH;

FIGS. 3A to 3C provide diagrams, each showing a first example ofdetermining a format, according to a first aspect of the presentinvention;

FIG. 4 is a diagram to show a second example of determining a format,according to the first aspect;

FIGS. 5A to 5C provide diagrams, each showing a third example ofdetermining a format, according to the first aspect;

FIGS. 6A and 6B provide diagrams, each showing an example of controllingthe RS density in format A, according to a second aspect of the presentinvention;

FIGS. 7A and 7B provide diagrams, each showing an example of controllingthe RS density in format A, according to the second aspect;

FIG. 8 is a diagram to show an example of controlling the timing to feedback HARQ-ACK, according to a third aspect of the present invention;

FIG. 9 is a diagram to show an example of controlling short PUCCHresources, according to a fourth aspect of the present invention;

FIG. 10 is a diagram to show an example of a schematic structure of aradio communication system according to the present embodiment;

FIG. 11 is a diagram to show an example of an overall structure of aradio base station according to the present embodiment;

FIG. 12 is a diagram to show an example of a functional structure of aradio base station according to the present embodiment;

FIG. 13 is a diagram to show an example of an overall structure of auser terminal according to the present embodiment;

FIG. 14 is a diagram to show an example of a functional structure of auser terminal according to the present embodiment; and

FIG. 15 is a diagram to show an example hardware structure of a radiobase station and a user terminal according to the present embodiment.

DESCRIPTION OF EMBODIMENTS

Future radio communication systems (for example, LTE Rel. 14, 15 and/orlater versions, 5G, NR, etc.) are under study for introducing multiplenumerologies (including, for example, subcarrier spacing and/or symbolduration), not a single numerology. For example, future radiocommunication systems may support multiple subcarrier spacings such as15 kHz, 30 kHz, 60 kHz and 120 kHz.

Also, future radio communication systems are being studied to introducetime units (referred to as, for example, “subframes,” “slots,”“minislots,” “subslots,” “TTIs,” “radio frames” and so on) that are thesame as and/or different than existing LTE systems (LTE Rel. 13 orearlier versions), while supporting multiple numerologies.

For example, a subframe is a time unit that has a predetermined timeduration (for example, one ms), regardless of what numerology a userterminal uses.

On the other hand, a slot is a time unit that is based on the numerologyused by the user terminal. For example, if the subcarrier spacing is 15kHz or 30 kHz, the number of symbols per slot may be seven or fourteen.Meanwhile, when the subcarrier spacing is 60 kHz or greater, the numberof symbols per slot may be fourteen. In addition, a slot may include aplurality of minislots (subslots).

Generally, subcarrier spacing and symbol duration hold a reciprocalrelationship. Therefore, as long as the number of symbols per slot (orminislot (subslot)) stays the same, the higher (wider) the subcarrierspacing, the shorter the slot length, and the lower (narrower) thesubcarrier spacing, the longer the slot length. Note that “subcarrierspacing is high” may be paraphrased as “subcarrier spacing is wide,” and“subcarrier spacing is low” may be paraphrased as “subcarrier spacing isnarrow.”

For such future radio communication systems, studies are on-going tosupport a UL control channel (hereinafter also referred to as a “shortPUCCH”) that is structured to be shorter in duration than the PUCCHformats of existing LTE systems (for example, LTE Rel. 13 and/or earlierversions) and/or a UL control channel (hereinafter also referred to as a“long PUCCH”) that is structured to have a longer duration than theabove short duration.

FIG. 1 provide diagrams, each showing an example of the format of a ULcontrol channel in future radio communication systems. FIG. 1A shows anexample of a short PUCCH, and FIG. 1B shows an example of a long PUCCH.As shown in FIG. 1A, a short PUCCH is arranged in a predetermined numberof symbols (here, one symbol) from the end of a slot. Note that thesymbol to arrange the short PUCCH is not confined to the end of a slot,and a predetermined number of symbols at the top or in the middle of aslot may be used as well. In addition, the short PUCCH may be placed inone or more frequency resources (for example, in one or more physicalresource blocks (PRBs)).

Also, the short PUCCH may be time-division-multiplexed and/orfrequency-division-multiplexed with a UL data channel (hereinafter alsoreferred to as “PUSCH”) in the slot. Also, the short PUCCH may betime-division-multiplexed and/or frequency-division-multiplexed with aDL data channel (hereinafter also referred to as “PDSCH”) and/or a DLcontrol channel (hereinafter also referred to as “PDCCH (PhysicalDownlink Control CHannel)”) in the slot.

With the short PUCCH, a multi-carrier waveform may be used (for example,the OFDM (Orthogonal Frequency Division Multiplexing) waveform), or asingle-carrier waveform may be used (for example, the DFT-s-OFDM(Discrete Fourier Transform-Spread-Orthogonal Frequency DivisionMultiplexing) waveform).

Meanwhile, as shown in FIG. 1B, a long PUCCH is arranged over aplurality of symbols in a slot so as to have improved coverage over ashort PUCCH. Referring to FIG. 1B, this long PUCCH is not placed in apredetermined number of symbols (here, one symbol) at the top of theslot, but can be placed in a predetermined number of symbols at the top.In addition, the long PUCCH may be constituted by fewer frequencyresources (for example, one or two PRBs) than a short PUCCH, so as toprovide a power-boosting effect.

Also, the long PUCCH may be frequency-division-multiplexed with a PUSCHin the slot. In addition, the long PUCCH may betime-division-multiplexed with a PDCCH in the slot. Furthermore, asshown in FIG. 1B, frequency hopping may be applied to the long PUCCH perpredetermined duration in the slot (for example, per minislot(subslot)). Also, the long PUCCH may be placed with a short PUCCH in thesame slot. With the long PUCCH, a single-carrier waveform may be used(for example, the DFT-s-OFDM waveform).

In addition, a short PUCCH may accommodate a plurality of formats that,for example, use different methods of multiplexing reference signals(which are referred to as “RSs,” and include, for example, the DM-RS,which is used to demodulate UCI, the SRS, and so on). FIG. 2 providediagrams, each showing an example of a short PUCCH. FIG. 2A shows aformat in which UCI and an RS are frequency-division-multiplexed(hereinafter also referred to as “format A”). Meanwhile, FIG. 2B shows aformat in which UCI and an RS are time-division-multiplexed (hereinafteralso referred to as “format B”).

Now, cases will be described below, with reference to FIGS. 2A and 2B,where the basic subcarrier spacing (also referred to as “normalsubcarrier spacing,” “reference subcarrier spacing,” etc.) is 15 kHz,and where a short PUCCH is constituted by one symbol provided at thisnormal subcarrier spacing. Note that the normal subcarrier spacing isnot limited to 15 kHz.

As shown in FIG. 2A, when format A is used, UCI and an RS are mapped todifferent frequency resources (for example, subcarriers) in one symbolof normal subcarrier spacing. Note that, although, in FIG. 2A, a shortPUCCH of format A is arranged in the last symbol in a slot of normalsubcarrier spacing, the arrangement position in the slot is not limitedto here. Format A may be formed with two or more symbols of normalsubcarrier spacing.

Format A, shown in FIG. 2A, can reduce the overhead of RSs easily, andtherefore is suitable for a larger UCI payload. Meanwhile, provided thatthe receiving process (for example, the FFT (Fast Fourier Transform),UCI demodulation, etc.) cannot be started until one symbol of normalsubcarrier spacing has been received completely, format A may not besuitable for achieving shorter processing latency (shorter latency).Also, in format A, a multi-carrier waveform (for example, the OFDMwaveform) may be used so as to allow frequency division multiplexing ofUCI and an RS.

Meanwhile, as shown in FIG. 2B, format B is designed so that multiplesymbols of a higher subcarrier spacing than the normal subcarrierspacing are arranged inside one symbol of normal subcarrier spacing. Informat B, UCI and an RS are time-division-multiplexed in these multiplesymbols provided of the high subcarrier spacing.

For example, in format B shown in FIG. 2B, two symbols of a subcarrierspacing of 30 kHz are arranged in a time period of one symbol of asubcarrier spacing of 15 kHz. In format B, UCI and an RS are both mappedin different symbols of a subcarrier spacing of 30 kHz. As shown in FIG.2B, by mapping an RS in a symbol before UCI, the receiving process (forexample, the demodulation of the UCI) can be started earlier.

With format B shown in FIG. 2B, it is possible to start the receivingprocess earlier than format A, and therefore format B is suitable forachieving shorter processing latency. Meanwhile, given that an RS needsto be arranged over the whole of a PRB that is allocated to a shortPUCCH, format B may not be suitable for a larger UCI payload.Furthermore, when format B is used, there is no need to transmit UCI andan RS in multiple carriers, so that it may be possible to prevent thepeak-to-average power ratio (PAPR) from increasing, by using asingle-carrier waveform (for example, the DFT-s-OFDM waveform).

Although not shown in the drawings, when using format B, four symbols ofa subcarrier spacing of 60 kHz or eight symbols of a subcarrier spacingof 120 kHz may be arranged in one symbol of a subcarrier spacing of 15kHz.

Thus, if multiple formats including format A and format B are supportedfor a short PUCCH, there is a possibility that a user terminal is unableto adequately control the transmission of UCI using this short PUCCH.So, the present inventors have worked on the method for adequatelycontrolling UCI transmission using a short PUCCH, and arrived at thepresent invention.

To be more specific, the present inventors have come up with ideas ofappropriately determining the format of a short PUCCH for use intransmitting UCI (the first aspect), adequately controlling the densityof RSs in this format (the second aspect), controlling the timing of UCIfeedback in accordance with this format (the third aspect), andcontrolling the resource for the short PUCCH in accordance with thisformat (the fourth aspect). Note that each of the first to the fourthaspects above may be implemented alone, or at least two of them may becombined.

Now, the present embodiment will be described below in detail. Assumethat, with the present embodiment, a user terminal supports one or moresubcarrier spacings (for example, 15 kHz, 30 kHz, 60 kHz, 120 kHz,etc.). A short PUCCH may be constituted by a predetermined number ofsymbols (for example, one to three symbols) of normal subcarrierspacing. Although the normal subcarrier spacing in the followingdescription will be 15 kHz, the normal subcarrier spacing is not limitedto this.

(First Aspect)

According to the first aspect of the present invention, a user terminaldetermines the format of a UL control channel for use in transmittingUCI (for example, a short PUCCH) from among a plurality of formats,including format A, in which UCI and an RS arefrequency-division-multiplexed (the first format), and format B, inwhich UCI and an RS are time-division-multiplexed (the second format).To be more specific, the user terminal may decide the above format basedon at least one of the type of the UCI (UCI type), the payload of theUCI (UCI payload) and physical layer signaling (L1 signaling).

Now, examples of determining the format of a short PUCCH based on eachof the UCI type, the UCI payload and physical layer signaling will bedescribed below, in detail, as first to third examples of determiningthe format. Note that at least two of the first to the third examples ofdetermining the format may be combined.

<First Example of Determining Format>

In the first example of determining the format, the user terminaldetermines the format of a short PUCCH based on the UCI type. Here, theUCI type refers to information representing the content of UCI that istransmitted from the user terminal, and is information to represent atleast one of, for example, a scheduling request (SR), controlinformation (HARQ-ACK) in response to DL data, channel state information(CSI), beam index information (BI) and a buffer status report (BSR).

For example, if the UCI type is HARQ-ACK and/or SR (hereinafter“HARQ-ACK/SR”) (not including CSI), the user terminal may select formatB, and transmit the HARQ-ACK/SR using a short PUCCH of this format B.

Also, if the UCI type is CSI (not including HARQ-ACK/SR), the userterminal may select format A, and transmit the CSI using a short PUCCHin this format A.

Also, when the UCI type is HARQ-ACK/SR and CSI, the user terminal mayselect format A or format B, and control the CSI to be transmittedand/or dropped based on the selected format (see (1), (1)′ and (2)below)).

(1) When selecting format B, the user terminal transmits HARQ-ACK/SRusing a short PUCCH of format B, and the user terminal may drop the CSIdepending on whether simultaneous transmission of UCI and data issupported or not. For example, if this simultaneous transmission is notsupported (or disabled), the user terminal may drop the CSI. On theother hand, if this simultaneous transmission is supported (or enabled),the user terminal may transmit the CSI by using a data resource (forexample, a PUSCH).

Also, (1)′ when selecting format B, the user terminal may decide, basedon the overall number of bits of HARQ-ACK/SR and CSI (for example,HARQ-ACK/SR and CSI that are bundled in at least one of the spacedirection, the frequency direction and the time direction), whether ornot to transmit all of the HARQ-ACK/SR and the CSI by using a shortPUCCH of format B.

For example, if the overall number of bits of these HARQ-ACK/SR and CSIis not larger than a predetermined threshold, the user terminal maymultiplex not only the HARQ-ACK/SR, but also the CSI, over format B, andtransmit this. When, on the other hand, the overall number of bits islarger than the predetermined threshold, as mentioned earlier, the userterminal may transmit the HARQ-ACK/SR using a short PUCCH of format B,and drop the CSI, or transmit the CSI using a data resource (forexample, a PUSCH). Here, the predetermined threshold may be, forexample, the payload of format B or a predetermined value that iscalculated based on this payload.

(2) When selecting format A, the user terminal may transmit theHARQ-ACK/SR and the CSI by using a short PUCCH of format A.

Note that one of above (1) (and/or above (1)′) and above (2) (that is,either format A or format B) may be configured in user terminal bycommand information (for example, higher layer signaling) from thenetwork (for example, a radio base station). Furthermore, one of above(1) and (1)′ (that is, whether or not CSI transmission is allowed informat B) may be configured in the user terminal by command information(for example, higher layer signaling) from the network.

Also, in the event CSI is dropped, if there are a plurality of CSIs (forexample, CSIs pertaining to a plurality of cells (component carriers(CCs)), it is possible to drop all of these multiple CSIs, or drop partof these multiple CSIs.

FIG. 3 provide diagrams, each showing a first example of determining theformat according to the first aspect. In FIGS. 3A to 3C, the UCI type inslot #0 is HARQ-ACK/SR, the UCI type in slot #1 is CSI, and the UCI typein slots #2 and #3 is HARQ-ACK/SR and CSI. In FIGS. 3A to 3C, a shortPUCCH is constituted by one symbol of normal subcarrier spacing (forexample, 15 kHz).

In slot #0 in FIGS. 3A to 3C, the UCI type is HARQ-ACK/SR, so thatformat B is selected. When format B is used, even before the one symbolof normal subcarrier spacing that constitutes the short PUCCH iscompletely received, the receiving process can be started using theDM-RS that is placed in one symbol of a higher subcarrier spacing (forexample, 30 kHz) than the normal subcarrier spacing. Consequently, theUCI, which imposes strict latency requirements, like HARQ-ACK, can betransmitted adequately. However, since the single-carrier waveform useddoes not allow the RS and the UCI to be frequency-division-multiplexed,the overhead is large.

Also, in slot #1 of FIGS. 3A to 3C, since the UCI type is CSI, format Ais selected. When format A is used, the RS overhead is small and thepayload can be increased, so that CSI, having a larger number of bitsthan HARQ-ACK/SR, can be transmitted properly. Also, the latencyrequirement for CSI is not strict compared to HARQ-ACK/SR, so that theuse of format A, in which the receiving process cannot be started beforeone symbol having normal subcarrier spacing is completely received, haslittle impact.

In slots #2 and #3 shown in FIGS. 3A to 3C, the UCI type is HARQ-ACK/SRand CSI, where, in slot #2, the total number of bits of the HARQ-ACK/SRand the CSI is not greater than a predetermined threshold, and, in slot#3, the total number of these bits is greater than the predeterminedthreshold. In FIGS. 3A, 3B and 3C, above (1), (1)′ and (2) areconfigured, respectively.

As shown in FIG. 3A, in the case of (1) above, in both of slot #2 andslot #3, the HARQ-ACK/SR is transmitted in a short PUCCH of format B,and the CSI is dropped or transmitted using a data resource (forexample, a PUSCH), regardless of the total number of bits of theHARQ-ACK/SR and the CSI.

Meanwhile, as shown in FIG. 3B, in the case of (1)′ above, in slot #2where the total number of bits of the HARQ-ACK/SR and the CSI is notgreater than a predetermined threshold, the HARQ-ACK/SR and the CSI aretransmitted in a short PUCCH of format B. On the other hand, in slot #3in which the total number of these bits is larger than the predeterminedthreshold, the HARQ-ACK/SR is transmitted in a short PUCCH of format B,and the CSI is dropped or transmitted using a data resource (forexample, a PUSCH).

As shown in FIG. 3C, in the case of (2) above, in both of slot #2 andslot #3, the HARQ-ACK/SR and the CSI are transmitted in a short PUCCH offormat A, regardless of the total number of bits of the HARQ-ACK/SR andthe CSI.

According to the first example of determining the format, it is possibleto appropriately determine the format of a short PUCCH based on the UCItype, so that it is possible to properly fulfill the requirements thatvary per UCI type (the requirements being, for example, reduced latencyin the event the UCI type is HARQ-ACK, increased capacity in the eventthe UCI type is CSI, etc.).

<Second Example of Determining Format>

According to a second example of determining the format, a user terminaldetermines the format of a short PUCCH based on the UCI payload. Here,the UCI payload refers to the overall number of bits of UCI that istransmitted using a short PUCCH.

For example, the user terminal can select format A or format B based onthe UCI payload and a predetermined threshold. The predeterminedthreshold may be configured in the user terminal based on commandinformation (for example, high layer signaling) from a radio basestation. The predetermined threshold may be, for example, the payload offormat B, or may be the value that is given by multiplying this payloadby a predetermined coefficient α (0≤α<1).

FIG. 4 is a diagram showing a second example of determining the formataccording to the first aspect. As shown in FIG. 4, if the UCI payload isless than a predetermined threshold, the user terminal may select formatB. On the other hand, if the UCI payload is larger than thepredetermined threshold, the user terminal may select format A.

According to the second example of determining the format, the radiobase station can choose achieving either reduced latency or increasedcapacity. For example, if it is more important to reduce the latency,the radio base station may schedule the DL data so that the payload ofHARQ-ACK feedback using a short PUCCH does not grow large (that is, theradio base station can limit the number of component carriers (CC) incarrier aggregation (CA)). As a result of this, HARQ-ACK can be fed backin format B.

On the other hand, if it is more important to increase the capacity, theradio base station may schedule the DL data so that the payload ofHARQ-ACK feedback using a short PUCCH grows large (that is, the radiobase station can increase the number of CCs in CA). As a result,HARQ-ACK can be fed back in format A.

<Third Example of Determining Format>

According to a third example of determining the format, a user terminaldetermines the format of a short PUCCH based on physical layersignaling. Here, physical layer signaling (L1 signaling) may refer to,for example, downlink control information (DCI) that is transmitted in aDL control channel. This DCI may be DCI (DL assignment) that is used toschedule DL data (for example, a PDSCH).

For example, the user terminal can select format A or format B based ona predetermined field value in the DCI. Also, when the UCI type isHARQ-ACK/SR and CSI, the user terminal may perform control so that theCSI is transmitted and/or dropped, in accordance with the selectedformat.

FIG. 5 provide diagrams, each showing the third example of determiningthe format according to the first aspect. Assume that, in FIGS. 5A and5B, the UCI type is HARQ-ACK/SR and CSI in slot #0 and slot #1. Also,assume that, in slot #0, the total number of bits of the HARQ-ACK andthe CSI is not greater than a predetermined threshold (for example, thepayload of format B or a value that is based on the payload), and that,in slot #1, the total number of these bits is greater than thepredetermined threshold.

FIG. 5A shows a case where a predetermined field value in DCI indicatesformat B. In this case, the user terminal transmits the HARQ-ACK/SRusing a short PUCCH of format B, and, the user terminal may drop the CSIdepending on whether simultaneous transmission of UCI and data issupported or not. For example, if this simultaneous transmission is notsupported (or disabled), the user terminal may drop the CSI. On theother hand, if this simultaneous transmission is supported (or enabled),the user terminal may transmit the CSI using a data resource (forexample, a PUSCH).

Similar to FIG. 5A, FIG. 5B shows a case where a predetermined fieldvalue in DCI indicates format B. Meanwhile, FIG. 5B is different fromFIG. 5A in that the user terminal determines whether or not to transmitall of the HARQ-ACK/SR and the CSI, using a short PUCCH of format B,based on the overall number of bits of the HARQ-ACK/SR and the CSI (forexample, HARQ-ACK/SR and CSI that are bundled in at least one of thespace direction, the frequency direction and the time direction).

As shown with slot #0 of FIG. 5B, when the total number of bits ofHARQ-ACK/SR and CSI is not greater than a predetermined threshold, theHARQ-ACK/SR and the CSI are transmitted in a short PUCCH of format B. Onthe other hand, when the total number of these bits is larger than thepredetermined threshold as shown with slot #1 of FIG. 5B, theHARQ-ACK/SR may be transmitted in a short PUCCH of format B, and the CSImay be dropped or transmitted using a data resource (for example, aPUSCH).

FIG. 5C shows a case where a predetermined field value in DCI indicatesformat A. In this case, regardless of the total number of bits ofHARQ-ACK/SR and CSI, in slot #0 and slot #1, the user terminal cantransmit the HARQ-ACK/SR and the CSI using a short PUCCH of format A.

According to the third example of determining the format, it is possibleto appropriately specify which format is to be applied to a short PUCCH,by using a predetermined field value in DCI, on the network side (forexample, in a radio base station).

(Second Aspect)

According to a second aspect of the present invention, a user terminalmay control the density of RSs in a short PUCCH in each format based onhigher layer signaling and/or physical layer signaling. Here, given theresources in which a short PUCCH is allocated, the density of RSs (RSdensity) refers to the resources (for example, resource elements (REs))where RSs are allocated, and may be referred to as “overhead” and/or thelike. Now, how the density of RSs is controlled in short PUCCH formats Aand B will be described in detail below.

<Format A>

When a user terminal uses a short PUCCH of format A, the RS density inthis format A may be (1) configured by higher layer signaling or (2)specified by physical layer signaling, or (3) a plurality of candidateresources for arranging RSs may be configured by higher layer signaling,and at least one of these multiple candidate resources may be specifiedby physical layer signaling.

FIG. 6 provide diagrams, each showing an example of controlling the RSdensity in format A according to the second aspect. In FIG. 6B, RSs arefrequency-division-multiplexed with UCI and arranged in a larger numberof resources than in FIG. 6A. Note that the RS densities shown in FIGS.6A and 6B are simply examples, and these are not limiting.

(1) When the RS density for format A is configured by higher layersignaling, the user terminal may place RSs in arrangement resources thatare configured by higher layer signaling, regardless of the UCI type,the UCI payload, the resource for the short PUCCH and the number of PRBsthat are used to transmit the short PUCCH.

(2) When the RS density for format A is specified by physical layersignaling (for example, a predetermined field value in DCI), the userterminal may place RSs in arrangement resources that are specified byphysical layer signaling, regardless of the UCI type, the UCI payload,the resource for the short PUCCH and the number of PRBs that are used totransmit the short PUCCH. Note that, as for the predetermined fieldvalue in DCI, a resource indicator for PUCCH resources (also referred toas “HARQ-ACK resource indicator,” “ARI (ACK/NACK Resource Indicator),”etc.) may be used.

(3) When the RS density for format A is specified by higher layersignaling and physical layer signaling, the user terminal may place RSsin arrangement resources that are specified by physical layer signaling,among a plurality of candidate resources configured by higher layersignaling.

The RS density for format A is not limited to explicit ways of reportingsuch as those described in above (1) to (3), and can be reported in animplicit manner as well. For example, the RS density for format A may beassociated with at least one of the UCI type, the UCI payload, theresource for the short PUCCH and so on.

<Format B>

When the user terminal uses a short PUCCH of format B, the RS density inthis format B may be (1) configured by higher layer signaling or (2)specified by physical layer signaling, or (3) a plurality of candidateresources for arranging RSs are configured by higher layer signaling,and at least one of these multiple candidate resources may be specifiedby physical layer signaling.

FIG. 7 provide diagrams, each showing an example of controlling the RSdensity in format B according to the second aspect. In FIGS. 7A and 7B,a short PUCCH is constituted by one symbol of normal subcarrier spacing(for example, 15 kHz), and an RS is multiplexed in one symbol of ahigher subcarrier spacing than the normal subcarrier spacing.

For example, in FIG. 7A, an RS is arranged in one symbol having asubcarrier spacing of 60 kHz, and, in FIG. 7B, an RS is arranged in onesymbol having a subcarrier spacing of 30 kHz. In FIG. 7B, an RS isarranged in one symbol having a lower (narrower) subcarrier spacing thanin FIG. 7A. As a result of this, the RS in FIG. 7B istime-division-multiplexed with UCI and arranged in a larger number ofresources than in FIG. 7A. Note that the RS densities and subcarrierspacings shown in FIGS. 7A and 7B are simply examples, and these are notlimiting.

(1) When the RS density for format B is configured by higher layersignaling, the user terminal may place RSs in arrangement resources thatare configured by higher layer signaling, regardless of the UCI type,the UCI payload, the resource for the short PUCCH and the number of PRBsthat are used to transmit the short PUCCH.

(2) When the RS density for format B is specified by physical layersignaling (for example, a predetermined field value in DCI), the userterminal may place RSs in arrangement resources that are specified byphysical layer signaling, regardless of the UCI type, the UCI payload,the resource for the short PUCCH and the number of PRBs that are used totransmit the short PUCCH. Note that, as for the predetermined fieldvalue in DCI, a resource indicator for PUCCH resources (also referred toas “HARQ-ACK resource indicator,” “ARI,” etc.) may be used.

(3) When the RS density for format B is specified by higher layersignaling and physical layer signaling, the user terminal may place RSsin arrangement resources that are specified by physical layer signaling,among a plurality of candidate resources configured by higher layersignaling.

The RS density for format A is not limited to explicit ways of reportingsuch as those described in above (1) to (3), and can be reported in animplicit manner as well. For example, the RS density for format B may beassociated with at least one of the UCI type, the UCI payload, theresource for the short PUCCH and so on.

According to the second aspect, the RS density in each short PUCCHformat can be controlled adequately on the network side (for example, aradio base station).

(Third Aspect)

According to a third aspect of the present invention, how to control thetiming to feed back HARQ-ACK (also referred to as “feedback timing,”“transmission timing,” etc.) will be described. Format A that has beendescribed above is suitable for increasing the capacity per short PUCCH,but is not suitable for shortening the processing time. On the otherhand, format B that has been described above is suitable for shorteningthe processing time, but is not suitable for increasing the capacity pershort PUCCH.

Accordingly, when format A is selected for HARQ-ACK, the feedback ofthis HARQ-ACK is delayed compared to format B. On the other hand, whenformat B is selected for HARQ-ACK, this HARQ-ACK is fed back quickly,compared to format A. For example, when DL data is received in slot #n,the earliest timing to provide feedback in response to this DL data is(1) slot #n+3 in the event of format A, and (2) slot #n+2 in the eventof format B.

Furthermore, when format A is selected for HARQ-ACK, the reschedulingand/or retransmission of the DL data are delayed compared to when formatB is selected.

Therefore, according to the third aspect, the user terminal may controlthe timing for HARQ-ACK feedback based on the short PUCCH format. To bemore specific, when HARQ-ACK is included in the UCI type, the userterminal may control the timing to feed back the HARQ-ACK based on theformat of the short PUCCH and a predetermined field value in DCI. ThisDCI may be, for example, DCI (DL assignment) that is used to schedule DLdata.

FIG. 8 is a diagram to show an example of controlling the timing ofHARQ-ACK feedback according to the third aspect. In FIG. 8, each valueof a predetermined field in DCI specifies, per format, the timing tofeed back HARQ-ACK, when DL data is received in slot #n (the offsetvalue to apply to slot #n). Note that, in FIG. 8, the predeterminedfield in DCI is two bits, but this may be one bit, or may be three bitsor more.

For example, the predetermined field value “00” in DCI is associatedwith the feedback timing n+A0 for format A and the feedback timing n+B0for format B. As mentioned earlier, since the latency (processing time)reduction effect of format A is less than that of format B, A0>B0 holds.The same relationship holds among the feedback timings n+A1 to n+A3 andthe feedback timings n+B1 to n+B3, which are associated with thepredetermined DCI field values “01” to “11.”

In this way, when the timing to feed back HARQ-ACK is indicatedexplicitly by a predetermined field value in DCI, even if thepredetermined field value is the same, the predetermined field value maybe interpreted differently depending on which short PUCCH format isselected by the user terminal or designated by the network. That is,even if DL data is received in same slot #n, HARQ-ACK in response tothis DL data may be fed back at different timings depending on theformat of the short PUCCH.

Note that, in FIG. 8, information to represent the feedback timings (forexample, A0 to A3 and B0 to B3 in FIG. 8), associated with eachpredetermined field value of DCI, provided per format, may be defined inadvance in the specification, or may be configured in user terminals byway of higher layer signaling.

According to the third aspect of the present invention, it is possibleto control, on the network side (for example, a radio base station), thetiming to feed back HARQ-ACK from a user terminal to timings associatedwith each short PUCCH format.

(Fourth Aspect)

With a fourth aspect of the present invention, control of short PUCCHresources will be described. According to the fourth aspect, a userterminal may control the resource for a short PUCCH for use intransmitting UCI based on the format of the short PUCCH.

Here, the resource for a short PUCCH may be at least one of a timeresource (for example, a symbol), a frequency resource (for example, aPRB), a space resource (for example, a layer) and a code resource (forexample, an orthogonal spreading code such as an OCC (Orthogonal CoverCode) and a cyclic shift value).

To be more specific, the user terminal may decide the resource for ashort PUCCH based on the format of the short PUCCH and a predeterminedfield value in DCI. The DCI may be, for example, DCI (DL assignment)that is used to schedule DL data.

FIG. 9 is a diagram to show an example of controlling short PUCCHresources, according to the fourth aspect. In FIG. 9, each value of apredetermined field in DCI specifies the resource for a short PUCCH,provided per format. Note that, in FIG. 9, the predetermined field inDCI is two bits, but this may be one bit, or may be three bits or more.

For example, the predetermined field value “00” in DCI is associatedwith the resource A0 for format A and the resource B0 for format B.Likewise, the predetermined field values “01” to “11” in DCI areassociated with resources A1 to A3 for format A and resources B1 to B3for format B, respectively.

In this way, when the resource for a short PUCCH is indicated explicitlyby a predetermined field value in DCI, even if the predetermined fieldvalue is the same, the predetermined field value may be interpreteddifferently depending on which short PUCCH format is selected by theuser terminal or designated by the network.

Note that, in FIG. 9, information to represent the resources (forexample, resources A0 to A3 and resources B0 to B3 in FIG. 9),associated with each predetermined field value in DCI, provided performat, may be defined in advance in the specification, or may beconfigured in user terminals by way of higher layer signaling.

According to the fourth aspect, it is possible to control short PUCCHresources on a per format basis, on the network side (for example, radiobase station).

(Other Aspects)

To portray yet another aspect of the present invention, control of UCItransmission in a slot in which a channel state sounding referencesignal (SRS) is transmitted will be described. The transmission of theSRS may be configured by higher layer signaling or may be specified byphysical layer signaling. In the event higher layer signaling isapplied, for example, the SRS may be configured in the last symbol, and,if a gap period is provided at the end of the slot, the SRS may beprovided in the closest position to the gap period.

Also, UCI and an SRS may be multiplexed. For example, in the eventformat B is used, if, in one symbol of normal subcarrier spacing (forexample, 15 kHz), multiple symbols of a higher (wider) subcarrierspacing than the normal subcarrier spacing (for example, four symbols ata subcarrier spacing of 60 kHz) are provided, UCI, and the DM-RS and theSRS that are to be used to demodulate this UCI may betime-division-multiplexed in different symbols of this higher subcarrierspacing. Also, in the event format A is used, the UCI, the DM-RS and theSRS may be frequency-division-multiplexed.

When a short PUCCH and an SRS are frequency-division-multiplexing, thesemay be transmitted at the same subcarrier spacing. In this case, theshort PUCCH and the SRS can be orthogonalized, so that the interferencethe SRS gives to the PUCCH can be reduced. In this case, the short PUCCHand the SRS can be transmitted by adjusting the subcarrier spacing ofthe SRS with the subcarrier spacing of the short PUCCH. Meanwhile, thesubcarrier spacing of the short PUCCH that isfrequency-division-multiplexed with the SRS may be determined based onwhat subcarrier spacing is configured for the SRS.

(Radio Communication System)

Now, the structure of a radio communication system according to thepresent embodiment will be described below. In this radio communicationsystem, each radio communication method according to the above-describedembodiments is employed. Note that the radio communication methodsaccording to the herein-contained aspects of the present invention maybe applied individually, or two or more of them may be combined andapplied.

FIG. 10 is a diagram to show an example of a schematic structure of aradio communication system according to the present embodiment. A radiocommunication system 1 can adopt carrier aggregation (CA) and/or dualconnectivity (DC) to group a plurality of fundamental frequency blocks(component carriers) into one, where the LTE system bandwidth (forexample, 20 MHz) constitutes one unit. The radio communication system 1may be also referred to as “SUPER 3G,” “LTE-A (LTE-Advanced),”“IMT-Advanced,” “4G,” “5G,” “FRA (Future Radio Access),” “NR (New RAT:New Radio Access Technology),” and so on.

The radio communication system 1 shown in FIG. 10 includes a radio basestation 11 that forms a macro cell C1, and radio base stations 12 a to12 c that are placed within the macro cell C1 and that form small cellsC2, which are narrower than the macro cell C1. Also, user terminals 20are placed in the macro cell C1 and in each small cell C2. A structurein which different numerologies are applied between cells and/or withincells may be adopted.

Here, “numerology” refers to communication parameters in the frequencydirection and/or the time direction (for example, at least one of thesubcarrier spacing (subcarrier interval), the bandwidth, the symbolduration, the time duration of CPs (CP duration), the subframe duration,the time duration of TTIs (TTI duration), the number of symbols per TTI,the radio frame structure, the filtering process, the windowing process,and so on). In the radio communication system 1, for example, subcarrierspacings of, for example, 15 kHz, 30 kHz, 60 kHz, and 120 kHz may besupported.

The user terminals 20 can connect with both the radio base station 11and the radio base stations 12. The user terminals 20 may use the macrocell C1 and the small cells C2, which use different frequencies, at thesame time, by means of CA or DC. Also, the user terminals 20 can executeCA or DC by using a plurality of cells (CCs) (for example, two or moreCCs). Furthermore, the user terminals can use license band CCs andunlicensed band CCs as a plurality of cells.

Furthermore, the user terminal 20 can perform communication using timedivision duplexing (TDD) or frequency division duplexing (FDD) in eachcell. A TDD cell and an FDD cell may be referred to as a “TDD carrier(frame configuration type 2),” and an “FDD carrier (frame configurationtype 1),” respectively.

Furthermore, in each cell (carrier), a single numerology may beemployed, or a plurality of different numerologies may be employed.

Between the user terminals 20 and the radio base station 11,communication can be carried out using a carrier of a relatively lowfrequency band (for example, 2 GHz) and a narrow bandwidth (referred toas an “existing carrier,” a “legacy carrier” and so on). Meanwhile,between the user terminals 20 and the radio base stations 12, a carrierof a relatively high frequency band (for example, 3.5 GHz, 5 GHz, 30 to70 GHz and so on) and a wide bandwidth may be used, or the same carrieras that used in the radio base station 11 may be used. Note that thestructure of the frequency band for use in each radio base station is byno means limited to these.

A structure may be employed here in which wire connection (for example,means in compliance with the CPRI (Common Public Radio Interface) suchas optical fiber, the X2 interface and so on) or wireless connection isestablished between the radio base station 11 and the radio base station12 (or between 2 radio base stations 12).

The radio base station 11 and the radio base stations 12 are eachconnected with higher station apparatus 30, and are connected with acore network 40 via the higher station apparatus 30. Note that thehigher station apparatus 30 may be, for example, access gatewayapparatus, a radio network controller (RNC), a mobility managemententity (MME) and so on, but is by no means limited to these. Also, eachradio base station 12 may be connected with the higher station apparatus30 via the radio base station 11.

Note that the radio base station 11 is a radio base station having arelatively wide coverage, and may be referred to as a “macro basestation,” a “central node,” an “eNB (eNodeB),” a “gNB (gNodeB),” a“transmitting/receiving point” and so on. Also, the radio base stations12 are radio base stations having local coverages, and may be referredto as “small base stations,” “micro base stations,” “pico basestations,” “femto base stations,” “HeNBs (Home eNodeBs),” “RRHs (RemoteRadio Heads),” “eNBs,” “gNBs,” “transmitting/receiving points” and soon. Hereinafter the radio base stations 11 and 12 will be collectivelyreferred to as “radio base stations 10,” unless specified otherwise.

The user terminals 20 are terminals to support various communicationschemes such as LTE, LTE-A, 5G, NR and so on, and may be either mobilecommunication terminals or stationary communication terminals.Furthermore, the user terminals 20 can perform inter-terminal (D2D)communication with other user terminals 20.

In the radio communication system 1, as radio access schemes, OFDMA(orthogonal Frequency Division Multiple Access) can be applied to thedownlink (DL), and SC-FDMA (Single-Carrier Frequency Division MultipleAccess) can be applied to the uplink (UL). OFDMA is a multi-carriercommunication scheme to perform communication by dividing a frequencybandwidth into a plurality of narrow frequency bandwidths (subcarriers)and mapping data to each subcarrier. SC-FDMA is a single-carriercommunication scheme to mitigate interference between terminals bydividing the system bandwidth into bands formed with one or continuousresource blocks per terminal, and allowing a plurality of terminals touse mutually different bands. Note that the uplink and downlink radioaccess schemes are not limited to the combinations of these, and OFDMAmay be used in UL.

Also, in the radio communication system 1, a multi-carrier waveform (forexample, the OFDM waveform) may be used, or a single-carrier waveform(for example, the DFT-s-OFDM waveform) may be used.

In the radio communication system 1, a DL shared channel (PDSCH(Physical Downlink Shared CHannel), which is also referred to as, forexample, a “DL data channel”), which is used by each user terminal 20 ona shared basis, a broadcast channel (PBCH (Physical Broadcast CHannel)),L1/L2 control channels and so on, are used as DL channels. User data,higher layer control information and SIBs (System Information Blocks)are communicated in the PDSCH. Also, the MIB (Master Information Block)is communicated in the PBCH.

The L1/L2 control channels include DL control channels (a PDCCH(Physical Downlink Control CHannel), an EPDCCH (Enhanced PhysicalDownlink Control CHannel) and so on), a PCFICH (Physical Control FormatIndicator CHannel), a PHICH (Physical Hybrid-ARQ Indicator CHannel) andso on. Downlink control information (DCI), including PDSCH and PUSCHscheduling information, is communicated by the PDCCH. The number of OFDMsymbols to use for the PDCCH is communicated by the PCFICH. The EPDCCHis frequency-division-multiplexed with the PDSCH and used to communicateDCI and so on, like the PDCCH. It is possible to communicate HARQretransmission control information (ACK/NACK) in response to the PUSCHusing at least one of the PHICH, the PDCCH and the EPDCCH.

In the radio communication system 1, a UL shared channel (PUSCH:Physical Uplink Shared CHannel, which is also referred to as “UL datachannel” and so on), which is used by each user terminal 20 on a sharedbasis, a UL control channel (PUCCH: Physical Uplink Control CHannel), arandom access channel (PRACH: Physical Random Access CHannel) and so onare used as UL channels. User data, higher layer control information andso on are communicated by the PUSCH. Uplink control information (UCI),including at least one of DL signal retransmission control information(A/N), channel state information (CSI) and so on, is communicated in thePUSCH or the PUCCH. By means of the PRACH, random access preambles forestablishing connections with cells are communicated.

<Radio Base Station>

FIG. 11 is a diagram to show an example of an overall structure of aradio base station according to the present embodiment. A radio basestation 10 has a plurality of transmitting/receiving antennas 101,amplifying sections 102, transmitting/receiving sections 103, a basebandsignal processing section 104, a call processing section 105 and acommunication path interface 106. Note that one or moretransmitting/receiving antennas 101, amplifying sections 102 andtransmitting/receiving sections 103 may be provided.

User data to be transmitted from the radio base station 10 to a userterminal 20 on DL is input from the higher station apparatus 30 to thebaseband signal processing section 104, via the communication pathinterface 106.

In the baseband signal processing section 104, the user data issubjected to transmission processes, including a PDCP (Packet DataConvergence Protocol) layer process, division and coupling of the userdata, RLC (Radio Link Control) layer transmission processes such as RLCretransmission control, MAC (Medium Access Control) retransmissioncontrol (for example, an HARQ (Hybrid Automatic Repeat reQuest)transmission process), scheduling, transport format selection, channelcoding, an inverse fast Fourier transform (IFFT) process and a precodingprocess, and the result is forwarded to each transmitting/receivingsections 103. Furthermore, downlink control signals are also subjectedto transmission processes such as channel coding and an inverse fastFourier transform, and forwarded to the transmitting/receiving sections103.

Baseband signals that are pre-coded and output from the baseband signalprocessing section 104 on a per antenna basis are converted into a radiofrequency band in the transmitting/receiving sections 103, and thentransmitted. The radio frequency signals having been subjected tofrequency conversion in the transmitting/receiving sections 103 areamplified in the amplifying sections 102, and transmitted from thetransmitting/receiving antennas 101.

The transmitting/receiving sections 103 can be constituted bytransmitters/receivers, transmitting/receiving circuits ortransmitting/receiving apparatus that can be described based on generalunderstanding of the technical field to which the present inventionpertains. Note that a transmitting/receiving section 103 may bestructured as a transmitting/receiving section in one entity, or may beconstituted by a transmitting section and a receiving section.

Meanwhile, as for UL signals, radio frequency signals that are receivedin the transmitting/receiving antennas 101 are each amplified in theamplifying sections 102. The transmitting/receiving sections 103 receivethe UL signals amplified in the amplifying sections 102. The receivedsignals are converted into the baseband signal through frequencyconversion in the transmitting/receiving sections 103 and output to thebaseband signal processing section 104.

In the baseband signal processing section 104, UL data that is includedin the UL signals that are input is subjected to a fast Fouriertransform (FFT) process, an inverse discrete Fourier transform (IDFT)process, error correction decoding, a MAC retransmission controlreceiving process, and RLC layer and PDCP layer receiving processes, andforwarded to the higher station apparatus 30 via the communication pathinterface 106. The call processing section 105 performs call processingsuch as setting up and releasing communication channels, manages thestate of the radio base station 10 and manages the radio resources.

The communication path interface section 106 transmits and receivessignals to and from the higher station apparatus 30 via a predeterminedinterface. Also, the communication path interface 106 may transmitand/or receive signals (backhaul signaling) with neighboring radio basestations 10 via an inter-base station interface (for example, aninterface in compliance with the CPRI (Common Public Radio Interface),such as optical fiber, the X2 interface, etc.).

In addition, the transmitting/receiving sections 103 transmit DL signals(including at least one of a DL data signal, a DL control signal and aDL reference signal) to the user terminal 20, and receive UL signals(including at least one of a UL data signal, a UL control signal and aUL reference signal) from the user terminal 20.

Furthermore, the transmitting/receiving sections 103 receive UCI fromthe user terminal 20 via a UL data channel (for example, the PUSCH) or aUL control channel (for example, a short PUCCH and/or a long PUCCH).This UCI may include at least one of an HARQ-ACK in response to a DLdata channel (for example, the PDSCH), CSI, an SR, a beam index (BI) anda buffer status report (BSR).

In addition, the transmitting/receiving sections 103 may transmitcontrol information (for example, DCI) that represents the format of aUL control channel (for example, a short PUCCH) via physical layersignaling (L1 signaling) (see the third example of determining theformat according to the first aspect).

In addition, the transmitting/receiving sections 103 may transmitcontrol information that represents the RS density in a UL controlchannel (for example, a short PUCCH), per format, via higher layersignaling and/or physical layer signaling (see the second aspect).

In addition, the transmitting/receiving sections 103 may transmitcontrol information (for example, DCI) that indicates the timing to feedback HARQ-ACK in a UL control channel (for example, a short PUCCH), performat, via physical layer signaling (L1 signaling) (see the thirdaspect).

In addition, the transmitting/receiving sections 103 may transmitcontrol information (for example, DCI) that indicates the resource for aUL control channel (for example, a short PUCCH), per format, viaphysical layer signaling (L1 signaling) (the fourth aspect).

FIG. 12 is a diagram to show an example of a functional structure of aradio base station according to the present embodiment. Note that,although FIG. 12 primarily shows functional blocks that pertain tocharacteristic parts of the present embodiment, the radio base station10 has other functional blocks that are necessary for radiocommunication as well. As shown in FIG. 12, the baseband signalprocessing section 104 has a control section 301, a transmission signalgeneration section 302, a mapping section 303, a received signalprocessing section 304 and a measurement section 305.

The control section 301 controls the whole of the radio base station 10.The control section 301 controls, for example, the generation of DLsignals by the transmission signal generation section 302, the mappingof DL signals by the mapping section 303, the receiving processes (forexample, demodulation) for UL signals by the received signal processingsection 304 and the measurements by the measurement section 305.

To be more specific, the control section 301 schedules user terminals20. To be more specific, the control section 301 may perform schedulingand/or retransmission control with respect to DL data and/or UL datachannels based on UCI (for example, CSI) from user terminals 20.

Also, the control section 301 may exert control so that the format of aUL control channel (for example, a short PUCCH) for use in transmittingUCI is selected from a plurality of formats, including format A (firstformat), in which UCI and an RS are frequency-division-multiplexed, andformat B (second format), in which UCI and an RS aretime-division-multiplexed, and control information (for example, DCI) torepresent this format is transmitted via physical layer signaling (seethe third example of determining the format according to the firstaspect).

Also, the control section 301 may exert control so that the RS densityin a UL control channel (for example, a short PUCCH) is determined, performat, and control information to represent this RS density istransmitted via higher layer signaling and/or physical layer signaling(see the second aspect).

Also, the control section 301 may exert control so that the timing tofeed back HARQ-ACK in a UL control channel (for example, a short PUCCH)is determined, per format, and control information (for example, DCI) torepresent this feedback timing is transmitted via physical layersignaling (L1 signaling) (see the third aspect).

Furthermore, the control section 301 may exert control so that theresource for a UL control channel (for example, a short PUCCH) isdetermined, per format, and control information (for example, DCI) torepresent this resource is transmitted via physical layer signaling (L1signaling) (see the fourth aspect).

The control section 301 may control the received signal processingsection 304 to perform the receiving process for UCI from the userterminal 20 in accordance with the format of the UL control channel.

The control section 301 can be constituted by a controller, a controlcircuit or control apparatus that can be described based on generalunderstanding of the technical field to which the present inventionpertains.

The transmission signal generation section 302 generates DL signals(including DL data signals, DL control signals, DL reference signals andso on) based on commands from the control section 301, and outputs thesesignals to the mapping section 303.

For the transmission signal generation section 302, a signal generator,a signal generation circuit or signal generation apparatus that can bedescribed based on general understanding of the technical field to whichthe present invention pertains can be used.

The mapping section 303 maps the DL signals generated in thetransmission signal generation section 302 to predetermined radioresources based on commands from the control section 301, and outputsthese to the transmitting/receiving sections 103. For the mappingsection 303, mapper, a mapping circuit or mapping apparatus that can bedescribed based on general understanding of the technical field to whichthe present invention pertains can be used.

The received signal processing section 304 performs receiving processes(for example, demapping, demodulation, decoding, etc.) of UL signalstransmitted from the user terminals 20 (including, for example, a ULdata signal, a UL control signal, a UL reference signal, etc.). To bemore specific, the received signal processing section 304 may outputsthe received signals, the signals after the receiving processes and soon, to the measurement section 305. In addition, the received signalprocessing section 304 performs UCI receiving processes based on the ULcontrol channel format commanded from the control section 301.

The measurement section 305 conducts measurements with respect to thereceived signals. The measurement section 305 can be constituted by ameasurer, a measurement circuit or measurement apparatus that can bedescribed based on general understanding of the technical field to whichthe present invention pertains.

Also, the measurement section 305 may measure the channel quality in ULbased on, for example, the received power (for example, RSRP (ReferenceSignal Received Power)) and/or the received quality (for example, RSRQ(Reference Signal Received Quality)) of UL reference signals. Themeasurement results may be output to the control section 301.

<User Terminal>

FIG. 13 is a diagram to show an example of an overall structure of auser terminal according to the present embodiment. A user terminal 20has a plurality of transmitting/receiving antennas 201 for MIMOcommunication, amplifying sections 202, transmitting/receiving sections203, a baseband signal processing section 204 and an application section205.

Radio frequency signals that are received in a plurality oftransmitting/receiving antennas 201 are each amplified in the amplifyingsections 202. Each transmitting/receiving section 203 receives the DLsignals amplified in the amplifying sections 202. The received signalsare subjected to frequency conversion and converted into the basebandsignal in the transmitting/receiving sections 203, and output to thebaseband signal processing section 204.

In the baseband signal processing section 204, the baseband signal thatis input is subjected to an FFT process, error correction decoding, aretransmission control receiving process, and so on. The DL data isforwarded to the application section 205. The application section 205performs processes related to higher layers above the physical layer andthe MAC layer, and so on. Also, the broadcast information is alsoforwarded to application section 205.

Meanwhile, the UL data is input from the application section 205 to thebaseband signal processing section 204. The baseband signal processingsection 204 performs a retransmission control transmission process (forexample, an HARQ transmission process), channel coding, rate matching,puncturing, a discrete Fourier transform (DFT) process, an IFFT processand so on, and the result is forwarded to each transmitting/receivingsection 203. The UCI is also subjected to at least one of channelcoding, rate matching, puncturing, a DFT process and an IFFT process,and the result is forwarded to each transmitting/receiving section 203.

The baseband signal that is output from the baseband signal processingsection 204 is converted into a radio frequency band in thetransmitting/receiving sections 203. The radio frequency signals thatare subjected to frequency conversion in the transmitting/receivingsections 203 are amplified in the amplifying sections 202, andtransmitted from the transmitting/receiving antennas 201.

Furthermore, the transmitting/receiving sections 203 receive the DLsignals (including DL data signals, DL control signals, DL referencesignals, etc.) of the numerology configured in the user terminal 20, andtransmits the UL signals (including UL data signals, UL control signals,UL reference signals, etc.) of the numerology.

In addition, the transmitting/receiving sections 203 transmit the UCI tothe radio base station 10 using a UL data channel (for example, PUSCH)or a UL control channel (for example, a short PUCCH and/or a longPUCCH).

In addition, the transmitting/receiving sections 203 may receive controlinformation (for example, DCI) that represents the format of a ULcontrol channel (for example, a short PUCCH) through physical layersignaling (L1 signaling) (see the third example of determining theformat according to the first aspect).

In addition, the transmitting/receiving sections 203 may receive controlinformation that represents the RS density in a UL control channel (forexample, a short PUCCH), per format, via higher layer signaling and/orphysical layer signaling (see the second aspect).

In addition, the transmitting/receiving sections 203 may receive controlinformation (for example, DCI) that indicates the timing to feed backHARQ-ACK in a UL control channel (for example, a short PUCCH), performat, via physical layer signaling (L1 signaling) (see the thirdaspect).

In addition, the transmitting/receiving sections 203 may receive controlinformation (for example, DCI) that indicates the resource for a ULcontrol channel (for example, a short PUCCH), per format, via physicallayer signaling (L1 signaling) (see the fourth aspect).

For the transmitting/receiving sections 203, transmitters/receivers,transmitting/receiving circuits or transmitting/receiving apparatus thatcan be described based on general understanding of the technical fieldto which the present invention pertains can be used. Furthermore, atransmitting/receiving section 203 may be structured as onetransmitting/receiving section, or may be formed with a transmittingsection and a receiving section.

FIG. 14 is a diagram to show an example of a functional structure of auser terminal according to the present embodiment. Note that, althoughFIG. 14 primarily shows functional blocks that pertain to characteristicparts of the present embodiment, the user terminal 20 has otherfunctional blocks that are necessary for radio communication as well. Asshown in FIG. 14, the baseband signal processing section 204 provided inthe user terminal 20 has a control section 401, a transmission signalgeneration section 402, a mapping section 403, a received signalprocessing section 404 and a measurement section 405.

The control section 401 controls the whole of the user terminal 20. Thecontrol section 401 controls, for example, the generation of UL signalsin the transmission signal generation section 402, the mapping of ULsignals in the mapping section 403, the UL signal receiving processes inthe received signal processing section 404, the measurements in themeasurement section 405 and so on.

Furthermore, the control section 401 controls the UL control channel tobe used to transmit UCI from the user terminal 20, based on explicitcommands from the radio base station 10 or implicit decisions in theuser terminal 20.

Furthermore, the control section 401 may decide the format for a ULcontrol channel (for example, a short PUCCH) for use in transmittingUCI, from a plurality of formats, including format A (first format), inwhich UCI and an RS are frequency-division-multiplexed, and format B(second format), in which UCI and an RS are time-division-multiplexed.

In addition, the control section 401 may decide the format for a ULcontrol channel (for example, short PUCCH) for use in transmitting UCIbased on at least one of the UCI type, the UCI payload and physicallayer signaling (see the first to the third examples of determining theformat according to the first aspect).

Furthermore, the control section 401 may exert control, based on theformat of a UL control channel (for example, a short PUCCH) for use intransmitting UCI, so that at least part of the UCI is dropped ortransmitted (see the first and third examples of determining the formataccording to the first aspect). For example, if the UCI type for formatB is HARQ-ACK/SR and UCI, the control section 401 may drop at least oneCSI, or transmit the CSI in a UL data channel (for example, a PUSCH).Also, when the total number of bits of HARQ-ACK/SR and UCI is not largerthan a predetermined threshold, the control section 401 may transmit allof the HARQ-ACK/SR and the UCI in a UL control channel (for example, ashort PUCCH) of format B.

In addition, the control section 401 may control the density ofreference signals in the format of a UL control channel (for example, ashort PUCCH) for use in transmitting UCI, based on higher layersignaling and/or physical layer signaling (see the second aspect).

In addition, the control section 401 may determine the timing to feedback HARQ-ACK based on the format of a UL control channel (for example,a short PUCCH) for use in transmitting UCI, and a predetermined fieldvalue in DCI (see the third aspect).

In addition, the control section 401 may decide the resource for a ULcontrol channel (for example, a short PUCCH) for use in transmitting UCIbased on the format of the UL control channel and a predetermined fieldvalue in DCI (see the fourth aspect).

For the control section 401, a controller, a control circuit or controlapparatus that can be described based on general understanding of thetechnical field to which the present invention pertains can be used.

In the transmission signal generation section 402, UL signals (includingUL data signals, UL control signals, UL reference signals, UCI, etc.)are generated (including, for example, encoding, rate matching,puncturing, modulation, etc.)

based on commands from the control section 401, and output to themapping section 403. For the transmission signal generation section 402,a signal generator, a signal generation circuit or signal generationapparatus that can be described based on general understanding of thetechnical field to which the present invention pertains can be used.

The mapping section 403 maps the UL signals generated in thetransmission signal generation section 402 to radio resources based oncommands from the control section 401, and output the result to thetransmitting/receiving sections 203. For the mapping section 403, amapper, a mapping circuit or mapping apparatus that can be describedbased on general understanding of the technical field to which thepresent invention pertains can be used.

The received signal processing section 404 performs receiving processes(for example, demapping, demodulation, decoding, etc.) of DL signals(including DL data signals, scheduling information, DL control signals,DL reference signals, etc.). The received signal processing section 404outputs the information received from the radio base station 10, to thecontrol section 401. The received signal processing section 404 outputs,for example, broadcast information, system information, high layercontrol information related to higher layer signaling such as RRCsignaling, physical layer control information (L1/L2 controlinformation) and so on, to the control section 401.

The received signal processing section 404 can be constituted by asignal processor, a signal processing circuit or signal processingapparatus that can be described based on general understanding of thetechnical field to which the present invention pertains. Also, thereceived signal processing section 404 can constitute the receivingsection according to the present invention.

The measurement section 405 measures channel states based on referencesignals (for example, CSI-RS) from the radio base station 10, andoutputs the measurement results to the control section 401. Note thatthe channel state measurements may be conducted per CC.

The measurement section 405 can be constituted by a signal processor, asignal processing circuit or signal processing apparatus, and ameasurer, a measurement circuit or measurement apparatus that can bedescribed based on general understanding of the technical field to whichthe present invention pertains.

<Hardware Structure>

Note that the block diagrams that have been used to describe the aboveembodiments show blocks in functional units. These functional blocks(components) may be implemented in arbitrary combinations of hardwareand/or software. Also, the means for implementing each functional blockis not particularly limited. That is, each functional block may berealized by one piece of apparatus that is physically and/or logicallyaggregated, or may be realized by directly and/or indirectly connectingtwo or more physically and/or logically separate pieces of apparatus(via wire or wireless, for example) and using these multiple pieces ofapparatus.

For example, the radio base station, user terminals and so on accordingto embodiments of the present invention may function as a computer thatexecutes the processes of the radio communication method of the presentinvention. FIG. 15 is a diagram to show an example of a hardwarestructure of a radio base station and a user terminal according to oneembodiment of the present invention.

Physically, the above-described radio base stations 10 and userterminals 20 may be formed as a computer apparatus that includes aprocessor 1001, a memory 1002, a storage 1003, communication apparatus1004, input apparatus 1005, output apparatus 1006 and a bus 1007.

Note that, in the following description, the word “apparatus” may bereplaced by “circuit,” “device,” “unit” and so on. Note that thehardware structure of a radio base station 10 and a user terminal 20 maybe designed to include one or more of each apparatus shown in thedrawings, or may be designed not to include part of the apparatus.

For example, although only one processor 1001 is shown, a plurality ofprocessors may be provided. Furthermore, processes may be implementedwith one processor, or processes may be implemented in sequence, or indifferent manners, on two or more processors. Note that the processor1001 may be implemented with one or more chips.

Each function of the radio base station 10 and the user terminal 20 isimplemented by reading predetermined software (program) on hardware suchas the processor 1001 and the memory 1002, and by controlling thecalculations in the processor 1001, the communication in thecommunication apparatus 1004, and the reading and/or writing of data inthe memory 1002 and the storage 1003.

The processor 1001 may control the whole computer by, for example,running an operating system. The processor 1001 may be configured with acentral processing unit (CPU), which includes interfaces with peripheralapparatus, control apparatus, computing apparatus, a register and so on.For example, the above-described baseband signal processing section 104(204), call processing section 105 and so on may be implemented by theprocessor 1001.

Furthermore, the processor 1001 reads programs (program codes), softwaremodules or data, from the storage 1003 and/or the communicationapparatus 1004, into the memory 1002, and executes various processesaccording to these. As for the programs, programs to allow computers toexecute at least part of the operations of the above-describedembodiments may be used. For example, the control section 401 of theuser terminals 20 may be implemented by control programs that are storedin the memory 1002 and that operate on the processor 1001, and otherfunctional blocks may be implemented likewise.

The memory 1002 is a computer-readable recording medium, and may beconstituted by, for example, at least one of a ROM (Read Only Memory),an EPROM (Erasable Programmable ROM), an EEPROM (Electrically EPROM), aRAM (Random Access Memory) and/or other appropriate storage media. Thememory 1002 may be referred to as a “register,” a “cache,” a “mainmemory” (primary storage apparatus) and so on. The memory 1002 can storeexecutable programs (program codes), software modules and/or the likefor implementing the radio communication methods according toembodiments of the present invention.

The storage 1003 is a computer-readable recording medium, and may beconstituted by, for example, at least one of a flexible disk, a floppy(registered trademark) disk, a magneto-optical disk (for example, acompact disc (CD-ROM (Compact Disc ROM) and so on), a digital versatiledisc, a Blu-ray (registered trademark) disk), a removable disk, a harddisk drive, a smart card, a flash memory device (for example, a card, astick, a key drive, etc.), a magnetic stripe, a database, a server,and/or other appropriate storage media. The storage 1003 may be referredto as “secondary storage apparatus.”

The communication apparatus 1004 is hardware (transmitting/receivingdevice) for allowing inter-computer communication by using wired and/orwireless networks, and may be referred to as, for example, a “networkdevice,” a “network controller,” a “network card,” a “communicationmodule” and so on. The communication apparatus 1004 may be configured toinclude a high frequency switch, a duplexer, a filter, a frequencysynthesizer and so on in order to realize, for example, frequencydivision duplex (FDD) and/or time division duplex (TDD). For example,the above-described transmitting/receiving antennas 101 (201),amplifying sections 102 (202), transmitting/receiving sections 103(203), communication path interface 106 and so on may be implemented bythe communication apparatus 1004.

The input apparatus 1005 is an input device for receiving input from theoutside (for example, a keyboard, a mouse, a microphone, a switch, abutton, a sensor and so on). The output apparatus 1006 is an outputdevice for allowing sending output to the outside (for example, adisplay, a speaker, an LED (Light Emitting Diode) lamp and so on). Notethat the input apparatus 1005 and the output apparatus 1006 may beprovided in an integrated structure (for example, a touch panel).

Furthermore, these pieces of apparatus, including the processor 1001,the memory 1002 and so on are connected by the bus 1007 so as tocommunicate information. The bus 1007 may be formed with a single bus,or may be formed with buses that vary between pieces of apparatus.

Also, the radio base station 10 and the user terminal 20 may bestructured to include hardware such as a microprocessor, a digitalsignal processor (DSP), an ASIC (Application-Specific IntegratedCircuit), a PLD (Programmable Logic Device), an FPGA (Field ProgrammableGate Array) and so on, and part or all of the functional blocks may beimplemented by the hardware. For example, the processor 1001 may beimplemented with at least one of these pieces of hardware.

Variations

Note that the terminology used in this specification and the terminologythat is needed to understand this specification may be replaced by otherterms that convey the same or similar meanings. For example, “channels”and/or “symbols” may be replaced by “signals (or “signaling”).” Also,“signals” may be “messages.” A reference signal may be abbreviated as an“RS,” and may be referred to as a “pilot,” a “pilot signal” and so on,depending on which standard applies. Furthermore, a “component carrier”(CC) may be referred to as a “cell,” a “frequency carrier,” a “carrierfrequency” and so on.

Furthermore, a radio frame may be comprised of one or more periods(frames) in the time domain. Each of one or more periods (frames)constituting a radio frame may be referred to as a “subframe.”Furthermore, a subframe may be comprised of one or more slots in thetime domain. A subframe may be a fixed time duration (for example, onems) not dependent on the numerology.

Furthermore, a slot may be comprised of one or more symbols in the timedomain (OFDM (Orthogonal Frequency Division Multiplexing) symbols,SC-FDMA (Single Carrier Frequency Division Multiple Access) symbols, andso on). Also, a slot may be a time unit based on numerology. Also, aslot may include a plurality of mini-slots. Each mini-slot may consistof one or more symbols in the time domain. Also, a mini-slot may bereferred to as a “subslot.”

A radio frame, a subframe, a slot, a mini-slot and a symbol allrepresent the time unit in signal communication. A radio frame, asubframe, a slot, a mini-slot and a symbol may be each called by otherapplicable names. For example, one subframe may be referred to as a“transmission time interval (TTI),” or a plurality of consecutivesubframes may be referred to as a “TTI,” or one slot or mini-slot may bereferred to as a “TTI.” That is, a subframe and/or a TTI may be asubframe (one ms) in existing LTE, may be a shorter period than one ms(for example, one to thirteen symbols), or may be a longer period oftime than one ms. Note that the unit to represent the TTI may bereferred to as a “slot,” a “mini slot” and so on, instead of a“subframe.”

Here, a TTI refers to the minimum time unit of scheduling in radiocommunication, for example. For example, in LTE systems, a radio basestation schedules the radio resources (such as the frequency bandwidthand transmission power that can be used in each user terminal) toallocate to each user terminal in TTI units. Note that the definition ofTTIs is not limited to this.

The TTI may be the transmission time unit of channel-encoded datapackets (transport blocks), code blocks and/or codewords, or may be theunit of processing in scheduling, link adaptation and so on. Note thatwhen a TTI is given, the period of time (for example, the number ofsymbols) in which transport blocks, code blocks and/or codewords areactually mapped may be shorter than the TTI.

Note that, when one slot or one mini-slot is referred to as a “TTI,” oneor more TTIs (that is, one or more slots or one or more mini-slots) maybe the minimum time unit of scheduling. Also, the number of slots (thenumber of mini-slots) to constitute this minimum time unit of schedulingmay be controlled.

A TTI having a time duration of one ms may be referred to as a “normalTTI (TTI in LTE Rel. 8 to 12),” a “long TTI,” a “normal subframe,” a“long subframe,” and so on. A TTI that is shorter than a normal TTI maybe referred to as a “shortened TTI,” a “short TTI,” “a partial TTI (or a“fractional TTI”), a “shortened subframe,” a “short subframe,” a“mini-slot,” “a sub-slot” and so on.

Note that a long TTI (for example, a normal TTI, a subframe, etc.) maybe replaced with a TTI having a time duration exceeding one ms, and ashort TTI (for example, a shortened TTI) may be replaced with a TTIhaving a TTI length less than the TTI length of a long TTI and not lessthan one ms.

A resource block (RB) is the unit of resource allocation in the timedomain and the frequency domain, and may include one or a plurality ofconsecutive subcarriers in the frequency domain. Also, an RB may includeone or more symbols in the time domain, and may be one slot, onemini-slot, one subframe or one TTI in length. One TTI and one subframeeach may be comprised of one or more resource blocks. Note that one ormore RBs may be referred to as a “physical resource block (PRB: PhysicalRB),” a “subcarrier group (SCG: Sub-Carrier Group),” a “resource elementgroup (REG),” a “PRB pair,” an “RB pair” and so on.

Furthermore, a resource block may be comprised of one or more resourceelements (REs). For example, one RE may be a radio resource field of onesubcarrier and one symbol.

Note that the structures of radio frames, subframes, slots, mini-slots,symbols and so on described above are merely examples. For example,configurations pertaining to the number of subframes included in a radioframe, the number of slots included in a subframe, the number ofmini-slots included in a slot, the number of symbols and RBs included ina slot or a mini-slot, the number of subcarriers included in an RB, thenumber of symbols in a TTI, the symbol duration, the length of cyclicprefixes (CPs) and so on can be variously changed.

Also, the information and parameters described in this specification maybe represented in absolute values or in relative values with respect topredetermined values, or may be represented in other informationformats. For example, radio resources may be specified by predeterminedindices. In addition, equations to use these parameters and so on may beused, apart from those explicitly disclosed in this specification.

The names used for parameters and so on in this specification are in norespect limiting. For example, since various channels (PUCCH (PhysicalUplink Control Channel), PDCCH (Physical Downlink Control Channel) andso on) and information elements can be identified by any suitable names,the various names assigned to these individual channels and informationelements are in no respect limiting.

The information, signals and/or others described in this specificationmay be represented by using a variety of different technologies. Forexample, data, instructions, commands, information, signals, bits,symbols and chips, all of which may be referenced throughout theherein-contained description, may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orphotons, or any combination of these.

Also, information, signals and so on can be output from higher layers tolower layers and/or from lower layers to higher layers. Information,signals and so on may be input and output via a plurality of networknodes.

The information, signals and so on that are input may be transmitted toother pieces of apparatus. The information, signals and so on to beinput and/or output can be overwritten, updated or appended. Theinformation, signals and so on that are output may be deleted. Theinformation, signals and so on that are input may be transmitted toother pieces of apparatus.

Reporting of information is by no means limited to theaspects/embodiments described in this specification, and other methodsmay be used as well. For example, reporting of information may beimplemented by using physical layer signaling (for example, downlinkcontrol information (DCI), uplink control information (UCI), higherlayer signaling (for example, RRC (Radio Resource Control) signaling,broadcast information (the master information block (MIB), systeminformation blocks (SIBs) and so on), MAC (Medium Access Control)signaling and so on), and other signals and/or combinations of these.

Note that physical layer signaling may be referred to as “L1/L2 (Layer1/Layer 2) control information (L1/L2 control signals),” “L1 controlinformation (L1 control signal)” and so on. Also, RRC signaling may bereferred to as “RRC messages,” and can be, for example, an RRCconnection setup message, RRC connection reconfiguration message, and soon. Also, MAC signaling may be reported using, for example, MAC controlelements (MAC CEs (Control Elements)).

Also, reporting of predetermined information (for example, reporting ofinformation to the effect that “X holds”) does not necessarily have tobe sent explicitly, and can be sent implicitly (by, for example, notreporting this piece of information).

Decisions may be made in values represented by one bit (0 or 1), may bemade in Boolean values that represent true or false, or may be made bycomparing numerical values (for example, comparison against apredetermined value).

Software, whether referred to as “software,” “firmware,” “middleware,”“microcode” or “hardware description language,” or called by othernames, should be interpreted broadly, to mean instructions, instructionsets, code, code segments, program codes, programs, subprograms,software modules, applications, software applications, softwarepackages, routines, subroutines, objects, executable files, executionthreads, procedures, functions and so on.

Also, software, commands, information and so on may be transmitted andreceived via communication media. For example, when software istransmitted from a website, a server or other remote sources by usingwired technologies (coaxial cables, optical fiber cables, twisted-paircables, digital subscriber lines (DSL) and so on) and/or wirelesstechnologies (infrared radiation, microwaves and so on), these wiredtechnologies and/or wireless technologies are also included in thedefinition of communication media.

The terms “system” and “network” as used herein are usedinterchangeably.

As used herein, the terms “base station (BS),” “radio base station,”“eNB,” “cell,” “sector,” “cell group,” “carrier,” and “componentcarrier” may be used interchangeably. A base station may be referred toas a “fixed station,” “NodeB,” “eNodeB (eNB),” “access point,”“transmission point,” “receiving point,” “femto cell,” “small cell” andso on.

A base station can accommodate one or more (for example, three) cells(also referred to as “sectors”). When a base station accommodates aplurality of cells, the entire coverage area of the base station can bepartitioned into multiple smaller areas, and each smaller area canprovide communication services through base station subsystems (forexample, indoor small base stations (RRHs: Remote Radio Heads)). Theterm “cell” or “sector” refers to part or all of the coverage area of abase station and/or a base station subsystem that provides communicationservices within this coverage.

As used herein, the terms “mobile station (MS)” “user terminal,” “userequipment (UE)” and “terminal” may be used interchangeably. A basestation may be referred to as a “fixed station,” “NodeB,” “eNodeB(eNB),” “access point,” “transmission point,” “receiving point,” “femtocell,” “small cell” and so on.

A mobile station may be referred to, by a person skilled in the art, asa “subscriber station,” “mobile unit,” “subscriber unit,” “wirelessunit,” “remote unit,” “mobile device,” “wireless device,” “wirelesscommunication device,” “remote device,” “mobile subscriber station,”“access terminal,” “mobile terminal,” “wireless terminal,” “remoteterminal,” “handset,” “user agent,” “mobile client,” “client” or someother suitable terms.

Furthermore, the radio base stations in this specification may beinterpreted as user terminals. For example, each aspect/embodiment ofthe present invention may be applied to a configuration in whichcommunication between a radio base station and a user terminal isreplaced with communication among a plurality of user terminals (D2D:Device-to-Device). In this case, user terminals 20 may have thefunctions of the radio base stations 10 described above. In addition,terms such as “uplink” and “downlink” may be interpreted as “side.” Forexample, an uplink channel may be interpreted as a side channel.

Likewise, the user terminals in this specification may be interpreted asradio base stations. In this case, the radio base stations 10 may havethe functions of the user terminals 20 described above.

Certain actions which have been described in this specification to beperformed by base station may, in some cases, be performed by uppernodes. In a network comprised of one or more network nodes with basestations, it is clear that various operations that are performed tocommunicate with terminals can be performed by base stations, one ormore network nodes (for example, MMEs (Mobility Management Entities),S-GW (Serving-Gateways), and so on may be possible, but these are notlimiting) other than base stations, or combinations of these.

The aspects/embodiments illustrated in this specification may be usedindividually or in combinations, which may be switched depending on themode of implementation. The order of processes, sequences, flowchartsand so on that have been used to describe the aspects/embodiments hereinmay be re-ordered as long as inconsistencies do not arise. For example,although various methods have been illustrated in this specificationwith various components of steps in exemplary orders, the specificorders that are illustrated herein are by no means limiting.

The aspects/embodiments illustrated in this specification may be appliedto LTE (Long Term Evolution), LTE-A (LTE-Advanced), LTE-B (LTE-Beyond),SUPER 3G, IMT-Advanced, 4G (4th generation mobile communication system),5G (5th generation mobile communication system), FRA (Future RadioAccess), New-RAT (Radio Access Technology), NR(New Radio), NX (New radioaccess), FX (Future generation radio access), GSM (registered trademark)(Global System for Mobile communications), CDMA 2000, UMB (Ultra MobileBroadband), IEEE 802.11 (Wi-Fi (registered trademark)), IEEE 802.16(WiMAX (registered trademark)), IEEE 802.20, UWB (Ultra-WideBand),Bluetooth (registered trademark), systems that use other adequate radiocommunication methods and/or next-generation systems that are enhancedbased on these.

The phrase “based on” as used in this specification does not mean “basedonly on,” unless otherwise specified. In other words, the phrase “basedon” means both “based only on” and “based at least on.”

Reference to elements with designations such as “first,” “second” and soon as used herein does not generally limit the number/quantity or orderof these elements. These designations are used only for convenience, asa method for distinguishing between two or more elements. Thus,reference to the first and second elements does not imply that only twoelements may be employed, or that the first element must precede thesecond element in some way.

The terms “judge” and “determine” as used herein may encompass a widevariety of actions. For example, to “judge” and “determine” as usedherein may be interpreted to mean making judgements and determinationsrelated to calculating, computing, processing, deriving, investigating,looking up (for example, searching a table, a database or some otherdata structure, ascertaining and so on. Furthermore, to “judge” and“determine” as used herein may be interpreted to mean making judgementsand determinations related to receiving (for example, receivinginformation), transmitting (for example, transmitting information),inputting, outputting, accessing (for example, accessing data in amemory) and so on. In addition, to “judge” and “determine” as usedherein may be interpreted to mean making judgements and determinationsrelated to resolving, selecting, choosing, establishing, comparing andso on. In other words, to “judge” and “determine” as used herein may beinterpreted to mean making judgements and determinations related to someaction.

As used herein, the terms “connected” and “coupled,” or any variation ofthese terms, mean all direct or indirect connections or coupling betweentwo or more elements, and may include the presence of one or moreintermediate elements between two elements that are “connected” or“coupled” to each other. The coupling or connection between the elementsmay be physical, logical or a combination thereof. For example,“connection” may be interpreted as “access.” As used herein, twoelements may be considered “connected” or “coupled” to each other byusing one or more electrical wires, cables and/or printed electricalconnections, and, as a number of non-limiting and non-inclusiveexamples, by using electromagnetic energy, such as electromagneticenergy having wavelengths in the radio frequency, microwave and opticalregions (both visible and invisible).

When terms such as “include,” “comprise” and variations of these areused in this specification or in claims, these terms are intended to beinclusive, in a manner similar to the way the term “provide” is used.Furthermore, the term “or” as used in this specification or in claims isintended to be not an exclusive disjunction.

Now, although the present invention has been described in detail above,it should be obvious to a person skilled in the art that the presentinvention is by no means limited to the embodiments described herein.The present invention can be implemented with various corrections and invarious modifications, without departing from the spirit and scope ofthe present invention defined by the recitations of claims.Consequently, the description herein is provided only for the purpose ofexplaining examples, and should by no means be construed to limit thepresent invention in any way.

The disclosure of Japanese Patent Application No. 2016-242218, filed onDec. 14, 2016, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

The invention claimed is:
 1. A terminal, comprising: a processor thatdetermines a format of an uplink (UL) control channel that is used totransmit an uplink control information (UCI), based on a number of bitsof the UCI, from a plurality of formats, including: a first format, inwhich the UCI and a demodulation reference signal arefrequency-division-multiplexed, and a second format, in which the UCIand the demodulation reference signal are time-division-multiplexed; anda transmitter that transmits the UCI.
 2. The terminal according to claim1, wherein if an overall number of bits of the UCI is greater than athreshold, the processor determines the first format.
 3. A radiocommunication method for a terminal comprising: determining a format ofan uplink (UL) control channel that is used to transmit an uplinkcontrol information (UCI), based on a number of bits of the UCI, from aplurality of formats, including: a first format, in which the UCI and ademodulation reference signal are frequency-division-multiplexed, and asecond format, in which the UCI and the demodulation reference signalare time-division-multiplexed; and transmitting the UCI.
 4. A basestation comprising: a receiver coupled to a processor, wherein thereceiver receives an uplink control information (UCI), and wherein aformat of an uplink (UL) control channel that is used to transmit theUCI is determined, based on a number of bits of the UCI, from aplurality of formats, including: a first format, in which the UCI and ademodulation reference signal are frequency-division-multiplexed, and asecond format, in which the UCI and the demodulation reference signalare time-division-multiplexed.
 5. A system comprising a terminal and abase station, wherein: the terminal comprises: a processor thatdetermines a format of an uplink (UL) control channel that is used totransmit an uplink control information (UCI), based on a number of bitsof the UCI, from a plurality of formats, including: a first format, inwhich the UCI and a demodulation reference signal arefrequency-division-multiplexed, and a second format, in which the UCIand the demodulation reference signal are time-division-multiplexed; anda transmitter that transmits the UCI, and the base station comprises: areceiver that receives the UCI.